Kahekili, July 2025
Time-series plot
Hourly climatology
DO vs pH
Depth vs salinity
Summary statistics
| Site | Temperature | Salinity | SAMIpH | Dissolved Oxygen |
|---|---|---|---|---|
| Control | 26.63 ± 0.68 (25.38 - 28.15) | 34.85 ± 0.11 (34.55 - 34.98) | 8.02 ± 0.04 (7.91 - 8.11) | 6.36 ± 0.9 (4.36 - 8.37) |
| Vent | 26.61 ± 0.46 (25.72 - 27.53) | 34.8 ± 0.08 (34.52 - 34.93) | NA ± NA (NA - NA) | 6.13 ± 0.9 (4.59 - 8.13) |
TCMs
Current data show a pronounced east-west current at Vent and S3, with stronger speeds at Vent. The control site is also characterized by stronger speeds albeit at more variable directions, mostly E-W and NE-SW.
Comparison of temperature sensors
Temperature measurements were compared between the MicroCAT, SAMI, miniDOT, and TCM at both Vent and Control sites.
An offset was calculated, i.e. instrument temperature - MicroCAT temperature. The time series plot of the offset shows a lower temperature reading from the SAMI sensor compared to the MicroCAT CTD.
The distribution plot of offset values shows a more consistent (narrower and taller peak) offset throughout the deployment for the SAMI and TCM instruments, unlike the miniDOT logger.
| Site | SAMI offset | miniDOT offset | TCM offset |
|---|---|---|---|
| Control | -0.09 ± 0.03 (-0.21 - 0.26) | 0.03 ± 0.03 (-0.08 - 0.22) | 0.02 ± 0.02 (-0.07 - 0.17) |
| Vent | NA ± NA (NA - NA) | 0.03 ± 0.04 (-0.15 - 0.15) | 0.04 ± 0.02 (-0.05 - 0.13) |
Figure 7. Density plot showing the distribution of offset values of each sensor during the deployment.
On average, the SAMI temperature is lower by 0.09 ºC from the MicroCAT temperature. This corresponds to a 0.0011 increase in pH (sd = 0.0003) when the SAMI temperature is used for calculating pH.
Accuracy, precision, and resolution of temperature probe of each instrument:
MicroCAT
Accuracy: ± 0.002 °C (-5 to +35 °C); ± 0.01 (+35 to +45 °C)
Resolution: 0.0001 °C
SAMI
Accuracy: ± 0.1 °C
Precision: ± 0.01 °C
Resolution: 0.01 °C
miniDOT
Accuracy: ± 0.1 °C
Resolution: 0.001 °C
TCM
Accuracy: ± 0.1 °C (-5 to +30 °C); ± 0.2 (+30 to +50 °C)
Resolution: 0.005 °C (-5 to +30 °C); ± 0.01 (+30 to +50 °C)
Comparison of MicroCAT and CastAway
Four sampling time points were available to compare the salinity and temperature measurements of MicroCAT and CastAway. Note that the CastAway deployment time was not in sync with the MicroCAT reading (15-min interval), hence the closest time point was chosen to compare with. Salinity was generally lower in CastAway, while its temperature was higher.
| Site | DateTime | Depth offset | Temperature offset | Salinity offset |
|---|---|---|---|---|
| Control | 2025-07-14 00:15:00 | 0.2110712 | 0.0171670 | -0.0585359 |
| Vent | 2025-07-14 12:15:00 | 0.1467954 | 0.0440655 | -0.0286851 |
| Control | 2025-07-15 00:45:00 | -0.0127528 | 0.1378205 | -0.1669344 |
| Vent | 2025-07-15 01:15:00 | 0.0935356 | 0.1196649 | -0.0531760 |
| Depth offset | Temperature offset | Salinity offset |
|---|---|---|
| 0.11 ± 0.09 (-0.01 - 0.21) | 0.08 ± 0.06 (0.02 - 0.14) | -0.08 ± 0.06 (-0.17 - -0.03) |
Accuracy, precision, and resolution of temperature, salinity, and pressure of each instrument:
MicroCAT
Temperature accuracy: ± 0.002 °C (-5 to +35 °C); ± 0.01 (+35 to +45 °C)
Temperature resolution: 0.0001 °C
Salinity accuracy: ± 0.01 (as shared by Chris of Sea-Bird) (0.003 mS/cm)
Salinity resolution: NA (0.0001 mS/cm)
Pressure accuracy: ± 0.02 dbar
Pressure resolution: 0.0004 dbar
CastAway
Temperature accuracy: ± 0.05 °C
Temperature resolution: 0.01 °C
Salinity accuracy: ± 0.1 (± 0.005 mS/cm)
Salinity resolution: 0.01 (0.001 mS/cm)
Pressure accuracy: ± 0.25 dbar
Pressure resolution: 0.01 dbar
Note that salinity is a tricky variable to determine its accuracy and precision since it is a function of conductivity, temperature, and pressure. Comparing each parameter accuracy of the two sensors, the MicroCAT will yield a more accurate salinity derivation (see here: https://blog.seabird.com/ufaqs/how-accurate-is-salinity-measured-by-my-ctd-what-factors-impact-accuracy/).